It's not easy to run any kind of restaurant in the Valley. But operating a seafood place has to be the toughest. That's because fresh fish furnishes so many opportunities to screw up. You don't have to be an old salt to know that frozen fish can't possibly match the taste and texture of the just-hooked variety. Demanding customers rightly insist that fish practically wriggle on the plate. And we don't want to hear excuses about Phoenix being in the desert, either. Because it's such a delicate product, fresh fish doesn't cut restaurant owners any slack. If a steak house cooks up too much meat today, there's a hash or stew special tomorrow. If a fish house miscalculates on the supply of ahi tuna, there's cat food tomorrow. What are some telltale signs that raise warning flags about the freshness of fish? Generally, experts say, avoid any fish if: 1. It's mounted and lacquered. 2. The species died out during the Pleistocene era. 3. Your cat tries to bury it. 4. It comes wrapped in a newspaper announcing the sinking of the Lusitania. And even if you know for certain your fish is only minutes out of the sea, that's still no guarantee of eating satisfaction. Cooking fish requires real skill. Just a couple of extra minutes under the broiler can turn a costly fillet into an expensive pile of mush. So given the potential for problems--quality control, expense, preparation--it's a wonder that most Valley seafood restaurant operators don't throw in the towel and open up a taco stand instead. I'm glad the Salt Cellar Restaurant's proprietors have resisted that temptation. It's an underground place, but in a literal, not bohemian, sense. You descend a steep staircase that eventually opens up into several below-street-level dining areas. For the most part, they're mercifully free of the fishing nets, tridents, buoys and hackneyed nautical gimcrackery that afflict seafood restaurants. Still, the dim lighting and black-egg-crate ceiling helped to promote the sensation of dining in a submarine.

This place has been around for decades, and a couple of visits made it clear to me why it has flourished. From food to service, everything runs swimmingly. Take the matter of seating. Unlike many restaurants these days, the Salt Cellar takes reservations seriously. Twice we made them during prime dining hours, and both times, the place was jammed. But no one waved us off to the bar or asked us to cool our heels. Instead, we were immediately led to a table. Once there, service was swift, friendly and knowledgeable. The staff here knows the menu, and makes recommendations you can trust. And when we left, the hostess, the server and the manager all thanked us for coming. It's astonishing how seductive such simple civilities as prompt seating, efficient service and a warm "good night" can be. I fell into such a good mood, I was prepared to give the food the benefit of every doubt. But I didn't have to. The Salt Cellar cooks up first-rate seafood meals. The appetizers are simple and scrumptious. Crab cakes are always a bit of a splurge, but the specimens here are worth it. They're sizzling, right out of the skillet, and bursting with crab. Smoked striped Hawaiian marlin is equally entertaining. Three thick, rich slices arrive lightly smoked from the Salt Cellar's own smoker. The halibut ceviche is a perfect summer starter, lots of butter-soft fish in a refreshing tomato-and-lemon broth. And the creamy New England clam chowder avoids the mucilaginous lumps that ruin so many of this town's other versions. The salad course is no throwaway, either. A sprightly lemon vinaigrette helps, and so does the fresh whole loaf of pumpernickel-rye bread from Scottsdale's Zurich bakery. I don't know how much this bread adds to the cost of the meal, but it's a pleasure to pay for it. The main dishes are expertly fashioned. On one occasion, my server talked up the swordfish, and he knew what he was talking about. It was sublime, broiled just right to juicy, ethereal weightlessness. And the kitchen was wise enough to season it with nothing more overpowering than air. If, like me, you prefer fish as close to a state of nature as possible, this swordfish is about as good as it gets. Cajun-blackened ahi tuna also displayed deft work. It was almost like eating steak--meaty flesh surrounding a juicy, pink interior--and just about as filling. The Salt Cellar is not a budget restaurant, so I'm happy to report that there's no stinting on portions.

I almost never order shrimp out anymore, even though I'm fond of it. But the dishes are too often overpriced and the preparations too often predictably dull. But the server so earnestly pleaded the cause of the shrimp San Remo special that I capitulated. I haven't felt this good about listening to somebody else's advice since my wife persuaded me to marry her. This marvelous platter features six big, firm black tiger shrimp saut‚ed in garlic and butter and festooned with sun-dried tomatoes and artichoke wedges. Everything sits on a bed of delightful artichoke pasta. If you've got a shrimp craving and $21.95, this is probably where you should be. Saut‚ed sea scallops are another excellent shellfish option. These eight moist beauties will transport you right to the New England shore. The Salt Cellar's go-withs show the same admirable attention to detail. Sure, you can get a baked potato, but the lemon-pecan rice medley has genuine flair. And you won't need any maternal prodding to finish the buttered-and-herbed steamed carrots and broccoli. Too bad no one will be hungry enough to appreciate dessert. The supplier-delivered desserts offer uncomplicated sweet-tooth satisfaction. Under less-filling circumstances, the Snickers cheesecake and the chocolate fudge cake could have been highlights. The Salt Cellar really seems to have its act together, both back in the kitchen and out front. Right now, I'm hooked. Fisher Kings Seafood and Market, 13802 North Scottsdale Road, Scottsdale, 998-7797. Hours: Lunch and Dinner, Monday through Saturday, 11 a.m. to 8:30 p.m. A combination retail outlet and restaurant, Fisher Kings features some of the freshest, best-looking filleted fish this side of the Seafood Market and Restaurant in Ahwatukee. There are only about ten tables here, and at dinnertime, cagey locals are apt to fill them up. It's not the atmosphere that's reeling them in. A refrigerated case displaying the catch of the day is the principal visual attraction. You can divert yourself for 30 seconds staring at a painting of an old sea captain and some shelves holding carved and painted Mexican fish. Fisher Kings' charms are on the plates, not the walls. Start off with a half-dozen oysters on the half-shell, so huge they're almost dangerous to slurp. But don't even think of ordering the starter of clam strips. Why would a place work so hard to earn a reputation for exquisite, fresh seafood, then offer an item that so clearly comes frozen right out of a 25-pound bag? This creates the kind of dissonance that can keep customers from coming back. Meals include soup or salad. Like the clam strips, neither comes close to the fish in quality. Seafood gumbo is pretty dull, lacking a briny kick. And the clam chowder, insufficiently creamy and flavorful, has only institutional appeal. About all you can say about the salad is it's green. But the kitchen does put out a pleasant basket of fresh-toasted garlic bread. The fish, though, is simply superb, most of it fashioned in a superheated convection oven designed to seal in the moistness.

The halibut practically made me swoon. It was cooked to a shimmering translucence; the juices spurted out the moment my fork touched the fish. Seasoned with a bit of lemon pepper, it's one of the few earthly pleasures I've enjoyed that's not illegal, immoral or fattening. In the same class are the Chilean sea bass, a beautiful, white, flaky slab; and the thick, meaty ahi tuna. Each tastes as if it were just plucked from the sea. And when you consider that the tuna retails for $11.99 per pound, the $11.95 dinner price (about a ten-ounce portion) is quite a bargain. Idaho trout also made a favorable impression, as did the saut‚ed shrimp and scallops. For $9.95, you get five shrimp and six scallops, gently sizzled in butter. (Incidentally, the shrimp had been frozen, I was told. It's almost impossible to get fresh shrimp in the Valley unless you drive it up yourself from Rocky Point.)

But like the soup and salad, the accompaniments don't do justice to the fish. Meals come with plain, steamed cauliflower and broccoli, and an odd, mayonnaise-free coleslaw. Both of these items are no doubt good for you. They sure tasted like it. You can't backslide nutritionally with the French fries, either. Fisher Kings doesn't fry them--instead, they're cooked in the hot-air oven. Some foods are simply not susceptible to low-fat, low-cal interpretations. French fries, I'm grieved to report, is one of them. When it comes to dessert, however, Fisher Kings' healthy-minded Scottsdale clientele is apparently willing to make a lifestyle exception. But the place offers only unremarkable, coffee-shop-style pies that definitely aren't worth the calories.

Despite the lackluster soups, salad, go-withs and dessert, Fisher Kings' high-quality seafood makes it a player among Valley fish restaurants. If this place ever puts the same effort into the rest of the menu as it does the fish, it could go right to the head of the class.